PROJECT SUMMARY/ABSTRACT Cerebral palsy (CP) is a neuromuscular disorder that affects approximately 800,000 individuals in the U.S. Low muscle volume, strength and quality, poor balance and limited participation in physical activity are significant concerns in children with CP because they are strongly linked to their high risk of chronic disease. Therefore, identifying effective treatment strategies that address these issues is imperative. One treatment that has re- ceived significant attention is high-frequency, low-magnitude vibration (HLV). However, studies examining the effect of HLV on muscle development, balance and physical activity in children with CP are lacking. Our long- term goal is to identify treatments that reduce the risk of chronic disease in children with CP. The overall objective of this application is to determine the effect of a daily HLV treatment on muscle volume, strength, and quality, as well as physical activity and balance in ambulatory children with CP. Our central hypothesis is that a daily HLV treatment will increase leg muscle volume and strength, reduce leg intramuscular fat, increase physical activity and improve balance in children with CP. To test the central hypothesis, we will pursue the following aims: 1) to determine the effect of a daily HLV treatment on muscle volume and muscle strength in ambulatory children with CP; 2) to determine the effect of a daily HLV treatment on muscle quality in ambulatory children with CP; 3) to determine the effect of a daily HLV treatment on physical activity in ambulatory children with CP; and 4) to determine the effect of a daily HLV treatment on balance in ambulatory children with CP. A randomized con- trolled trial with one treatment arm will be used to accomplish the aims. Muscle volume and intramuscular fat in the leg will be assessed using magnetic resonance imaging. Muscle strength of the leg plantar flexors will be assessed using a dynamometer. Physical activity will be assessed using activity monitors. Balance will be assessed using measures of standing postural sway, as well as tests of fall recovery. HLV will be administered 10 min/d for 6 months. The proposed study is significant because children with CP have small, weak and fat- infiltrated muscles, poor balance and low physical activity which places them at a high risk for developing chronic disease. We propose an innovative intervention utilizing HLV and a comprehensive assessment of muscle prop- erties, balance and physical activity in children with CP. We expect to determine that HLV increases muscle size, strength and quality, physical activity and balance in children with CP. The results of the study will have a positive impact as they will serve as a key step toward establishing the effectiveness of HLV as treatment to combat the high risk of chronic disease in children with CP.